2,3-butanediol is an alcohol (represented by CH3CHOHCHOHCH3) having four carbons and two hydroxyl (—OH) groups and can be chemically and catalytically converted into 1,3-butadiene, which is a raw material for preparation of synthetic rubbers, and methyl ethyl ketone (MEK), which is a fuel additive and a solvent. 2,3-butanediol is a very important industrial intermediate since 2,3-butanediol can be used as an octane booster through mixing with gasoline.
2,3-butanediol can be produced by chemical synthesis and microbial fermentation. However, due to high production costs, 2,3-butanediol has not been produced on a commercially viable scale. In recent years, with rapid development of techniques for producing 2,3-butanediol through microbial fermentation, fossil fuel price increase and tightened international regulations on environmental contamination, there has been a growing focus on the importance of finding biological methods for producing 2,3-butanediol through microbial fermentation.
Since 2,3-butanediol includes two stereocenters, 2,3-butanediol can be found in three stereoisomers, namely, a D(−) form (levo form, 2R,3R-BDO), an L(+) form (dextro form, 2S,3S-BDO), and a meso form (2R,3S-BDO). 2,3-butanediol having optical activity together with the aforementioned general applicability of 2,3-butanediol can have special applications. For example, D(−) 2,3-butanediol can be used as an anti-freeze agent since it has a very low freezing point. Further, D(−) 2,3-butanediol can be used as an intermediate for medicines and agricultural compounds. However, production of optically pure D(−) 2,3-butanediol through chemical synthesis is not preferred because synthesis and separation/purification thereof are costly. Production of optically pure D(−) 2,3-butanediol through microbial fermentation is economically advantageous (Zeng et al., Curr. Opin. Biotechnol., 22:6, 2011).
Bio-based production of 2,3-butanediol can be made by a great variety of microorganisms through microbial fermentation and representative examples of such microorganisms include microorganisms belonging to genus Enterobacter, genus Klebsiella, genus Bacillus, genus Serratia, and the like. Naturally occurring wild type microorganisms have drawbacks in that they mainly produce meso-2,3-butanediol having no optical activity, or even if they could produce 2,3-butanediol isomers having optical activity, the isomers are produced in the form of a mixture.
Paenibacillus polymyxa can produce D(−) 2,3-butanediol with high purity. However, Paenibacillus polymyxa requires expensive nutrient components and has low productivity and yield, and thus has a problem in that it cannot be directly applied to the current industrialized processes.
As a result of earnest investigation aimed at developing a recombinant microorganism having optical activity allowing it to be used in industrialized processes and capable of producing D(−) 2,3-butanediol, the present inventors identified that a recombinant microorganism in which a specific gene is deleted/substituted produces high purity D(−) 2,3-butanediol with high productivity and yield. Based on this finding, the present invention has been completed.